In recent years, optical discs as represented by DVDs and Blu-ray discs are widely used as inexpensive and portable information recording media, and an optical disc recording device configured to additionally record data on optical discs such as DVD-Rs and BD-Rs as recordable information recording media has been put into practical use.
The optical disc recording device of this type is configured such that a light beam is irradiated onto a guide groove (a groove) or onto a prepit of a concave-and-convex shape which has been preformed in a track of an optical disc, and information (an address) on the track of the optical disc is acquired, using a reproduction signal to be obtained based on reflected light from the guide groove or from the prepit.
Further, the optical disc is constructed such that the guide groove is wobbled at a predetermined cycle. The optical disc recording device is configured such that a light beam is irradiated onto a rotating optical disc, and a signal component corresponding to the cycle of the wobble is extracted, using a reproduction signal to be obtained based on reflected light from the guide groove. The optical disc recording device acquires a timing signal at which data is to be recorded i.e. a recording clock signal by applying a signal processing such as PLL (Phase Locked Loop) to the extracted signal component.
Furthermore, generally, a block constituting an error-correction code is used as a base unit for the recording unit of data. The optical disc recording device performs a recording operation of data in the unit of blocks, referring to a position on a track correlated to position information.
For instance, a recording operation onto DVD-R is performed using a recording clock signal which is synchronized with a wobble, referring to position information acquired based on a reproduction signal from a prepit (a land prepit) of a concave-and-convex shape. Blocks are directly connected to each other, and data is sequentially written in the blocks. Accordingly, in the case where data is newly recorded on an optical disc in which data has already been recorded, an extremely high-precision recording position control is required so that discontinuity such as data interruption or data overwriting may not occur in a portion where already-recorded data and data to be newly recorded are written and connected to each other.
Heretofore, there have been proposed various techniques, as techniques for realizing high-precision recording position control at a portion where two data are written and connected to each other (see e.g. patent literature 1 and patent literature 2).
In the information recording device disclosed in patent literature 1, in additionally recording new data, the phase of a clock signal for a writing operation is synchronized with the phase of a clock signal for a reproducing operation of written data, and then, the frequency of the writing clock signal is recovered to a frequency unique to the writing clock signal at a predetermined time constant for avoiding generation of phase displacement at a portion where two data are written and connected to each other.
The optical disc device disclosed in patent literature 2 is configured such that a displacement amount between the position where data has been recorded and the position where the data is to be recorded is detected, and the frequency of a recording clock is controlled in such a manner as to eliminate displacement between the position at which the trailing end of new data is recorded, and the position at which the trailing end of new data is to be recorded in recording the new data. With this arrangement, the recording position of new data is adjusted, and accumulation of recording position displacement is avoided.
FIG. 13 is a diagram showing a configuration of the conventional optical disc device disclosed in patent literature 2. In the following, only the elements in the conventional optical disc device that are related to the invention are described.
The first timer 801 has a first counter that increments the count value by one in synchronism with a recording clock. The count value of the first counter is preset to a predetermined value (F) in response to a prepit sync detection signal, without depending on the state (an activated state or a non-activated state) of a recording gate signal.
The second timer 802 has a second counter that increments the count value by one in synchronism with a recording clock. The count value of the second counter is preset to a predetermined value (G) in response to a data sync detection signal, as far as the recording gate signal is in a non-activated state.
The subtractor 803 outputs a difference signal indicating a difference between the value of the first timer 801 and the value of the second timer 802.
The filter 29 restricts a time change amount of the difference signal to be outputted from the subtractor 803, and outputs a difference signal containing the restricted time change amount to the PLL 30, as a correction amount signal.
The PLL 30 controls the frequency of the recording clock in such a manner that the correction amount signal is approximated to zero level (in other words, the difference between the value of the first timer 801 and the value of the second timer 802 is set to “0”).
In this way, new data is recorded, referring to a data sync detection signal in a portion where previously recorded data and data to be newly recorded are connected to each other. With this arrangement, it is possible to secure continuity between the previously recorded data and the data to be newly recorded. Further, even if the previously recorded data is displaced from the position where the data is to be recorded, the displacement amount is detected, and the frequency of a recording clock is controlled in accordance with the detected displacement amount. Thus, there is no likelihood that displacement of a recording position may remain.
Further, there has also been proposed a technique, wherein a buffer area is formed in a portion where the blocks are connected to each other so as to lower the demand of precisely positioning the recording position, and the data format is revised in such a manner as to eliminate a clearance between the blocks by overlapping the recording end of a preceding block and the recording start of a succeeding block with each other in the buffer area (see e.g. patent literature 3).
On the other hand, as disclosed in patent literature 4, there has been proposed a technique, wherein a reflection film is formed on a concave-convex mark preformed in accordance with modulated main information, and an additionally recordable mark is formed by irradiating laser light at an interval longer than the period corresponding to a longest mark of the concave-convex mark for changing the optical characteristic of the reflection film, whereby sub information synchronized with the main information is recorded in a superimposed manner.
All the techniques disclosed in patent literatures 1 through 3 have been proposed based on the premise that a recording clock signal is obtained with respect to a wobbled groove which has been preformed in a track. The technique disclosed in patent literature 4 has been proposed based on the premise that a recording clock signal is obtained with respect to a preformed concave-convex mark.
The conventional optical disc devices as described above have the following drawbacks to overcome.
In the arrangement disclosed in patent literature 1, although continuity in a portion where previously recorded data and new data are written and connected to each other can be secured, the positional displacement amount of the previously recorded data is carried to the new data, and positional displacement of recording data based on position information derived from a wobble or a prepit cannot be eliminated.
In the arrangement disclosed in patent literature 2, the frequency of a recording clock is corrected in such a manner that recording position displacement is eliminated at the recording end of new data, based on the positional displacement detection amount on recorded data. However, in the case where the frequency of a recording clock becomes unstable during a recording operation of new data, it is impossible to eliminate recording position displacement that may newly occur.
In the arrangement disclosed in patent literature 3, it is possible to avoid generation of a blank portion in a boundary portion between recording end of a preceding block and recording start of a succeeding block by forming a buffer area which overlaps the preceding block and the succeeding block. However, it is impossible to avoid generation of a blank portion that cannot be absorbed by forming an overlap portion of a predetermined length or to avoid generation of data overwriting in a portion between preceding and succeeding blocks that cannot be absorbed in the buffer area, at the recording end position, in the case where recording position displacement over the length of the overlap portion has occurred, or in the case where recording position displacement over the length of the buffer area has occurred, during an operation of sequentially recording new data in blocks.
In the arrangement disclosed in patent literature 4, it is required to reproduce position information from a concave-and-convex pit for obtaining a recording clock signal. As a result, as compared with a case where a recording clock signal is obtained from a continuous wobbled groove, a frequency displacement of a recording clock signal is likely to occur with respect to a defect on an optical disc or with respect to deterioration of S/N ratio of a reproduction signal.
Further, the S/N ratio of a reproduction signal is deteriorated, because the light amount of reflected light from an optical disc is also changed during a period when the light intensity of laser light is modulated, as a recording operation is proceeded. In particular, since the light intensity of laser light is modulated for a period longer than the period corresponding to a longest mark of the concave-convex mark, the S/N ratio of a reproduction signal may be intermittently deteriorated during a recording operation, with the result that the forming position of an additionally recordable mark may be displaced.